The present invention generally relates to components and materials suitable for use in high temperature applications, such as gas turbine engines. More particularly, this invention is directed to assemblies with joints subjected to high temperatures and wear-resistant coating systems for such joints.
Higher operating temperatures for gas turbine engines are continuously sought in order to increase their efficiency. Significant advances in high temperature capabilities have been achieved through the formulation of iron, nickel and cobalt-base superalloys, whose high temperature properties enable components to withstand long exposures to operating temperatures within the compressor, turbine, combustor and augmentor sections of high-performance gas turbine engines. Certain components that require attachment with articulating joints create design challenges in view of the high temperatures, vibration and corrosive environment within a gas turbine engine. For example, pins, trunnions and other components employed to pivotably secure other components must have physical properties that are compatible with adjacent components and exhibit resistance to contact wear and corrosion over long durations at high temperatures.
FIG. 1 schematically represents an assembly 10 comprising an articulating joint defined by a pin 12 that pivotably supports a component 14 (represented in cross-section) to allow the component 14 to pivot about the axis of the pin 12. As an example, the pin 12 may be a hinge pin for a flapper valve, such as of the type used in gas turbine engines to regulate the cooling air flow to air-cooled turbine components. The diametric clearance between the pin 12 and component 14 is exaggerated for purposes of illustration. As schematically represented in FIG. 1, the shank 16 of the pin 12 has been severely worn as a result of the pivoting motion and vibration of the component 14 relative to the pin 12. Wear has primarily occurred on the shank 16 of the pin 12, though it is foreseeable that the inverse situation could exist. Localized damage to the wear surfaces of the pin 12 and component 14 can be accelerated by the effects of corrosion within the hostile environment of the turbine engine.
In one particular application, flapper valves formed of the nickel-base alloy Inconel (IN) 625 (nominal composition of, by weight, about 21.5% chromium, about 9.0% molybdenum, about 3.6% niobium 2.5% iron, about 0.2% aluminum, about 0.2% titanium, about 0.2% manganese, about 0.2% silicon, about 0.05% carbon, the balance nickel and incidental impurities) have been observed to rapidly wear when secured with a hinge formed of the cobalt-base alloy L-605 (HA25) (nominal composition of, by weight, about 20.0% chromium, about 10.0% nickel, about 15.0% tungsten, and about 0.5% carbon, the balance cobalt and incidental impurities). Though this combination of materials has been very reliable in gas turbine engine applications, more severe operating conditions have lead to more rapid wear rates, while simultaneously a longer wear life has been sought for the assembly.
A wide variety of coating materials are known and widely used to protect components of gas turbine engines, including hard impact and erosion-resistant coating materials such as nitrides and carbides. For example, see U.S. Pat. No. 4,904,528 to Gupta et al. (titanium nitride (TiN) coatings), U.S. Pat. No. 4,839,245 to Sue et al. (zirconium nitride (ZrN) coatings), U.S. Pat. No. 4,741,975 to Naik et al. (tungsten carbide (WC) and tungsten carbide/tungsten (WC/W) coatings), U.S. Pat. No. 7,186,092 to Bruce et al. (combinations of tantalum carbide (TaC), niobium carbide (NbC), titanium carbide (TiC), titanium aluminum chromium carbide (TiAlCrC), titanium aluminum chromium nitride (TiAlCrN), titanium aluminum nitride (TiAlN), titanium aluminum carbide (TiAlC), and boron carbide (B4C)) and U.S. Published Patent Application Nos. 2009/0011195 and 2010/0078308 to Bruce et al. (combinations of TiAlN, chromium nitride (CrN) and titanium silicon carbonitride (TiSiCN)). However, these coating materials are primarily intended to promote the impact and erosion resistance of blades, as opposed to surfaces continuously subjected to contact wear.
Wear-resistant coatings intended for surfaces subject to contact wear have also been proposed for use in the high-temperature environment of gas turbine engines. Examples include thermal sprayed coatings of chromium carbide and Co—Mo—Cr—Si alloys, such as the commercially-available TRIBALOY® T400 and T800 alloys. These wear-resistant materials have also been applied as foils, as taught in U.S. Pat. No. 6,398,103 to Hasz et al. Nonetheless, there is an ongoing need for improved material combinations that would enable pivot joint assemblies to exhibit longer service lives in the hostile environment of a gas turbine engine.